A switched beam system is a system where a number of fixed directional beams are defined and a transceiver selects the directional beam that provides the greatest signal quality and the least interference. The use of a directional beam with a wireless transmit/receive unit (WTRU) requires signal level measurements on each of the directional beams to select the best directional mode of the switched beam antenna.
The WTRU monitors the received signal level for each of the directional beams, and reselects the best directional beam to accommodate environment changes and movement of the WTRU. In a CDMA2000 system, measurements are performed in the forward pilot channel which is continuously transmitted by each cell.
While transmitting/receiving data is performed using the (best) selected antenna beam, the WTRU also performs measurements in the selected antenna beam. However, to insure that the best beam is being used, the WTRU needs to monitor other antenna beams during operation. Switching to another antenna beam to perform measurements may cause data loss. This is because the data transmission/reception in the other antenna beams will be affected by the antenna beam pattern. The difference between the antenna gain from beam to beam can be very high.